This invention relates to the production, maintenance and resotration of concrete pavements and more particularly to pavements and paving operations involving the overlaying of asphaltic concrete on non-asphaltic concrete.
In this specification and the following claims, the term "cement concrete" will be used to refer to pavements of the kind in which rock particles of various sizes are joined by a binder, such as Portland cement or the like, that does not soften upon being heated to high temperatures. The term "asphaltic concrete" will be used to designate essentially thermoplastic concretes in which rock particles are bound by asphalt or an equivalent substance that can be softened to a liquid or semi-liquid state by being heated and which reharden upon cooling.
Paved highways, roads, bridge decks, aircraft landing runways and the like formed of cement concrete deteriorate after a period of time most notably by developing cracks which tend to enlarge. Slight cracks or incipient cracks may occur initially during the original curing of the concrete. Others may be initiated by thermal expansion and contraction effects or by impacts and uneven pressures from heavy vehicles or other causes. Cracks, including those which are initially very small, tend to enlarge and deepen over a period of time in part from the effects of repeated freezing and thawing of water which accumulates in the cracks.
While this progressive cracking is undesirable in any concrete pavement, it is a particularly serious problem in connection with concretes which contain steel reinforcing elements or the like. When cracks progress to the point where water may reach the reinforcement elements, rusting can greatly weaken the load-resisting capability of the concrete. Loss of structural strength from rusting of reinforcement elements is a very serious problem in bridge decks, although the problem is not limited to that particular context.
Many of the extensive conrete roadways and bridge decks which have been built in the recent past in the United States of America and elsewhere are exhibiting serious deterioration from cracking and surface irregularities and will eventually have to be replaced at great cost and effort unless better techniques for restoration and maintenance are developed.
Using known methods, concrete deterioration can be inhibited to a limited extent and worn concrete can be temporarily resealed by applying any of a variety of hardenable liquid sealants to the surface to inhibit water intrusion into cracks. The effectiveness of this process as heretofore practiced is very limited, particularly if the pavement is subjected to heavy use. Such sealants apparently do not penetrate as deeply and completely into cracks and other openings as would be desirable and the sealant itself may deteriorate rapidly.
Attempts have also been made to cast a dispersion of small wax beads within the concrete with the intention that after some deterioration has occurred, the concrete may be heated to liquefy the wax and that the wax will then flow into the interior openings of the concrete and reharden and reseal the pavement. This also has not proved satisfactory possibly because of the limited mobility of the liquefied wax or possibly because of the difficulties of deeply heating pavement with conventional heating methods.
Probably the most common prior method for addressing the problem discussed above has been to reseal and resurface the deteriorated cement concrete pavement by applying an overlayer of asphaltic concrete. While this accomplishes the desired result for a limited period of time, asphaltic concrete is itself subject to cracking and general deterioration with the result tha the problem soon reappears. Further resealing and resurfacing of such a composite pavement at that point, using known techniques, is a very costly and timeconsuming process at best.